Accelerator for vulcanization of rubber



Patented May 22, 1934 U TE STATE TENT orrics ACCELERATOR FORVULCANIZATION OF RUBBER Max H. Zimmermann, Rye, N. H., assignor to TheFirestone Tire & Rubber Company, Akron, Ohio,

a corporation of Ohio June 30, 1930 18 Claims.

This invention relates to accelerators for the vulcanization or curingof rubber compounds.

There have heretofore been known a large number of nitrogen and nitrogensulfur-containing compounds for accelerating vulcanization of rubber ofwhich diphenylguanidine disclosed in Weiss PatentNo.1,411,231,andmercapto-benzo-thiazole described by Jacobson andFrankenbaker, Ber. 24, 1400 (1891), respectively may be 0 cited asexamples. These compounds when added to the rubber mix beforevulcanization improve the properties of the product and shorten the timeof cure.

In the utilization of a number of the abovementioned compounds there hasbeen a distinct disadvantage in that the accelerating power of thenitrogen or nitrogen sulfur compound becomes effective during thecompounding or processing of the raw rubber so that the latter is set 2up or partially vulcanized in the mill, calender 'or tubing machine, orother apparatus in which the compounds are handled.

Accordingly in the present invention this disadvantage is avoided sincethe accelerator herein described does not begin to act to anyappreciable extent to bring about the vulcanization of the rubber untilthe latter has been heated to approximately the vulcanizing temperature,the temperature of rubber during the processing or compounding being ata considerably lower temperature than that used during vulcanization.

This application is a continuation of my copending application SerialNo. 424,446 filed January 29, 15430.

The accelerator devised and employed in accordance with the presentinvention is specifically the reaction product of amercapto-aryl-thiazole and formaldehyde.

A method of producing this accelerator is by boiling together amercapto-aryl-thiazole, for

example mercapto-benzo-thiazole with a formaldehyde solution, as forexample commercial 46% formaldehyde. The molecular proportion offormaldehyde being in excess of the molecular equivalent of themercapto-benzo-thiazole. Upon prolonged heating themercapto-benzo-thiazole is converted into an oily product which uponcooling solidifies into a crystalline mass, which is a mixture ofmercapto-benzo-thiazole and the reaction product thereof withformaldehyde. The formaldehyde water solution of the reaction product,however, upon cooling yields a pure crystalline reaction product ofmercapto-benzothiazole and formaldehyde.

A modified method is to dissolve the mercaptobenzo-thiazole in a mixtureof alcohol and solution of formaldehyde by applying heat, theproportions used being as follows: 17 parts of mercaptobenzo-thiazole;17 parts of alcohol and 10 parts of 40% formaldehyde solution. Themixture is brought to boiling point in a closed vessel provided with areflux condenser. After the mixture has boiled for a sufficient periodto completely dissolve the mercapto-benzo-thiazole the mixture isallowed to cool, whereupon a substantially pure crystalline reactionproduct will crystallize out and which may be filtered from the motherliquor. The latter may then be used for a succeeding batch or may bedistilled to recover the alcohol This stock, vulcanized by heatingsamples thereof at varying times in a press under temperatures of 235 F.and 280 F., and tested, resulted in the following data:

Modulus at Tensile at Time of cure at 235 F. 000% elonbreak in gg zg ggation lbs/in.

30 min 110 745 840 60 min 740 2320 770 00 min 1050 2700 745 120 min 12052860 725 At 280 F.

15 m'n 1040 2335 720 30 min 1070 2480 720 min 1095 2640 735 00 min 10302670 740 The above results show the desirable accelerating properties ofthe new reaction product and further show that a retarding of theacceleration is accomplished. Acceleration of the vulcanization processis substantially delayed in curing rubber compounds using the newreaction product as compared with the action of previously known typesof accelerators, this fact being indicated by the low state of curewhich resulted after vulcanizing for thirty minutes at the lowtemperature 235 F.

The example above given is to be understood as merely illustrative ofone rubber compound which may be formed with the new accelerator and isnot to be considered limitative of the scope of the invention.Equivalent methods of manufacturing the new accelerator and ofcompounding the accelerator to produce a new vulcanized rubber compoundwill be apparent to those skilled in the art to which this inventionpertains.

It will further be understood that other mercapto-aryl-thiazoles thanmercapto-benzo-thiazole may be used in the reaction with formaldehyde toobtain products in accordance with the present invention. Thus, forexample mercaptotolyl-thiazoles, mercapto-Xylylthiazoles,mercapto-naphthyl-thiazoles and homologs thereof when reacted upon byformaldehyde will produce equally effective accelerators.

Various other modifications may be resorted to without departing fromthe spirit of the invention or the scope of the appended claims.

What is claimed is:

1. The reaction product of a mercapto-arylthiazole and formaldehyde, thearyl radical being a member of the benzene series.

2; The reaction product of mercapto-benzothiazole and formaldehyde.

3. The process of producing a rubber vulcam ization accelerator whichcomprises treating a mercapto-aryl-thiazole with formaldehyde underreacting conditions, the aryl radical being a member of the benzeneseries.

4. The process of producing a rubber vulcanization accelerator whichcomprises treating a mercapto-aryl-thiazole with an aqueous solution offormaldehyde, the aryl radical being a member of the benzene series.

5. The process of producing a rubber vulcanization accelerator whichcomprises heating a mixture of a mercapto-aryl-thiazole and an aqueoussolution of formaldehyde, the aryl radical being a member of the benzeneseries.

6. The process of producing a rubber vulcanization accelerator whichcomprises heating a mixture of a mercapto-aryl-thiazole and an aqueoussolution of formaldehyde, and cooling to crystallize out the reactionproduct, the aryl radical being a member of the benzene series.

'7. The process of producing a rubber vulcanization accelerator whichcomprises heating a mercapto-aryl-thiazole with alcohol and an aqueoussolution of formaldehyde, the aryl radical being a member of the benzeneseries.

8. The process of producing a rubber vulcanization accelerator whichcomprises treating mercapto-benzo-thiazole with formaldehyde underreacting conditions.

9. The process of producing a rubber vulcanization accelerator whichcomprises treating mercapto-benzo-thiazole with an aqueous solution offormaldehyde.

10. The process of producing a rubber vulcanization accelerator whichcomprises heating a mixture of mercapto-benzo-thiazole and an aqueoussolution of formaldehyde.

11. The process of producing a rubber vulcanization accelerator whichcomprises heating a mixture of mercapto-benzo-thiazole and an aqueoussolution of formaldehyde, and cooling to crystallize out the reactionproduct.

12. The process of producing a rubber vulcanization accelerator whichcomprises heating mercapto-benzo-thiazole with alcohol and an aqueoussolution of formaldehyde.

13. A process of manufacturing vulcanized rubber which comprises heatingrubber and a vulcanization agent in the presence of an acceleratorcomprising the reaction product of a mercapto-aryl-thiazole andformaldehyde, the aryl radical being a member of the benzene series.

14. A process of manufacturing vulcanized rubber winch comprises heatingrubber and a vulcanization agent in the presence of an acceleratorcomprising the reaction product of mercapto-benzo-thiazole andformaldehyde.

15. A vulcanized rubber product prepared by heating a mixture of rubberand sulfur in the presence of a vulcanization accelerating compositioncomprising a reaction product of a mercapto-aryl-thiazole andformaldehyde, the aryl radical being a member of the benzene series.

16. A vulcanized rubber product prepared by heating a mixture of rubberand sulfur in the presence of a vulcanization accelerating compositioncomprising a reaction product of mercapto-benzo-thiazole andformaldehyde.

17. The process of effecting the curing of rubber which consists inbringing together under reacting conditions formaldehyde and amercapto-aryl-thiazole to form a vulcanization ac celerator,incorporating the accelerator in a rubber mix and vulcanizing the same,the aryl radical being a member of the benzene series.

18. The process of eiiecting the curing of rubber which consists inbringing together under reacting conditions formaldehyde andmercaptobenzo-thiazole to form a vulcanization accelerator,incorporating the accelerator in a rubber mix and vulcanizing the same.

NIAX H. ZIMMERMANN.

